IMHO, if it was my daughter, I'd be seeking a used brand name, 250cc or better.
I did a quick search
http://www.cycletrader.com/Honda-Hel...ix&vrsn=hybrid
many are priced well, and dont be fearful of a Honda with 20,000 miles on it.
The parts are easy to get, a set of new rollers and belt, are cheap, new tires are fairly cheap.
My Honda BR, will hold 65mph and will get into the 70's range, so theres plenty of power for highway use.
IF you live in a hilly area, consider any brands of the 400cc scooters. Light weight and agile, with way more power, even if she dont use it, she has it at the crack of the throttle.
Best wishes to you both.